1. Field of the Invention
This invention relates to turbine arrangements for gas turbine engines, and particularly to a new and improved turbine arrangement wherein the radial axes of the turbine blades and stator vanes are arranged to be substantially normal to the mean flow streamline of the gases flowing through the turbine.
2. Description of the Prior Art
The annular gas flowpath within the turbine section of a gas turbine engine often includes a portion which is sloped outwardly away from the longitudinal axis of the engine. The sloped arrangement permits the turbine rotor blades which are disposed within the flowpath to be at a greater radial distance from the engine longitudinal axis, and thus have a longer moment arm and higher tangential velocities, than would the rotor blades in a nonsloped or reduced-slope flowpath. The longer moment arm allows lower aerodynamic loading thus permitting a more efficient transfer of aerodynamic energy from the gases in the flowpath to the turbine rotor.
However, the rotor blades and stator vanes within the highly sloped portion of the flowpath in prior art turbines remain aligned such that their radial axes are perpendicular to the engine longitudinal axis. Thus, the hot gases flowing through the sloped portion of the turbine flowpath encounter the blades and vanes at an angle other than at the normal. As a result, a spanwise flow of gases toward the radially outer ends of the rotor blades is induced. Such a configuration causes tip losses, that is, some of the gases tend to escape around tips of the rotor blades rather than flowing across the blades in a chordwise direction. This phenomenon is similar to the tip losses which occur off highly sweptback wings on aircraft. Such tip losses in the turbine reduce engine efficiency by reducing the amount of work available to rotate the turbine rotor. To make up for the tip losses, the engine must be operated at higher temperatures to produce more hot gases, with a corresponding increase in fuel consumption and decrease in engine life.
Another problem encountered in prior turbines is that the maximum amount of tip losses due to flowpath slope which are acceptable within a turbine sets a structural limitation to the degree of slope which can be built into the turbine flowpath. For the reasons indicated earlier, however, it may be desirable to have a flowpath with a slope greater than that limitation. Thus, a conflict exists between the desired degree of flowpath slope and the engine efficiency decrease due to tip losses caused by flowpath slope.
In view of the above-mentioned problems, it is therefore an object of the present invention to provide a turbine arrangement for reducing rotor blade tip losses and thereby increasing engine efficiency in turbines having a highly sloped gas flowpath.
Another object of the present invention is to provide a turbine arrangement in which the degree of slope of the gas flowpath can be increased beyond that in current engines without exceeding the limit of maximum acceptable tip losses.